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Block 4 > Main, Extraction and Auxiliary Steam > Flashcards

Main, Extraction and Auxiliary Steam Flashcards

1
Q

What are the functions of the Main Steam System?

A
  • Supply steam to the Turbine Generator, MSR’s, Main Condenser Air Ejectors (Hoggers), Gland Seal, Aux steam, and the steam driven Aux Feed Pump.
  • Provide CNMT isolation during a LOCA or MSLR
  • Provide RCS heat removal capability using the ADV’s and SBCS
  • Also supplies the Main Condenser Waterbox Priming Ejectors
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2
Q

What is 0% and 100% Main Steam Pressures?

A

100% Power ~ 850 psia
0% Power ~ 900 psia due to ramped TC and Tave programs

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3
Q

What are the functions of the Steam Flow Venturis?

A

Provides steam flow indication for:
1) Feed Water Control System,
2) RTGB Indication,
3) SBCS for Load reject Quick Open 1,
4) DCS Calorimetric
Secondary function would be to limit break flow due to a steamline rupture.
Located inside CNMT as close to the SG as possible.

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4
Q

What are the purposes of the Atmospheric Dump Valves?

A
  • Provide decay heat removal and cooldown capability when the MSIV’s are shut
  • Control primary plant temperature by controlling Steam Generator pressure during startup and shutdown
  • Designed to cooldown the RCS from full power to 350F at 75F/hr
  • Each Unit has the same combined capacity of 8% of the full power Steam Flow
  • Prevents a release to the environment in the event of a primary to secondary leak
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5
Q

How many ADVs are there and what is their capacity?

A

Unit 1
* 2 ADV’s - (1 per header)
* 4% capacity each.

Unit 2
* 4 ADV’s (2 per header)
* 2% capacity each

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6
Q

What is the normal ADV setpoint?

A
  • Auto setpoint normally ~ 900 psia,
  • Controller normally kept in “Manual” with valves closed
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7
Q

What is the motive force for the ADVs?

A

Unit 1
* Air Operated
* Air operated – Instrument Air normally not available following a LOOP without operator action to restore.

Unit 2
* Motor Operated

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8
Q

What are the ADV failure modes?

A

Unit 1
* Fails closed on a loss of power
* Fails closed on air
* Must be operated locally

Unit 2
* If DC power is lost – Fails As-Is in all modes
* If AC power is lost, must operate in manual mode
* If RED pressure setpoint bar is failed low, then no AC power to PIC/Modutronic unit
* If AC power regained in Auto-Man, PIC output restored-valve doesn’t move
* If AC power is regained in Auto-Auto, valve goes to position dictated by setpoint
* If PIC fails hi/low without losing power, ADV will go open or closed on setpoint

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9
Q

Where can ADVs be operated from?

A

Unit 1
* Control Room – RTGB 102
* N/A
* Hot Shutdown Panel – Using Normal/Isolate switches in SWGR rooms – alarm if aligned
* Locally via a valve handwheel when air is not available.

Unit 2
* Control Room – RTGB 102 (ADV’s: MV-08-18A & 18B) (Isolation Valves: MV-08-14 & 16)
* PACB-2 (ADV’s: MV-08-19A & 19B) (Isolation Valves: MV-08-15 & 17). Control is functionally the same as at RTGB-202, except the power supply trains are reversed
* Remote Shutdown Panel – Using Normal/Isolate switches in SWGR rooms – alarm if aligned to HSCP

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10
Q

Describe the ADV isolation valves.

A

Unit 1
* Each ADV has a manually operated, locked open isolation valve.

Unit 2
* DC powered MOV (1 per ADV, 4 total), Normally operated from RTGB key switch – Closed / Locked Open.
* Can also be operated locally via handwheel
* The isolation valves are normally in the LOCKED OPEN position; the only position in which the key can be removed
* Each ADV has an upstream DC powered motor-operated isolation valve; MV-08-14, 15, 16 and 17
* Powered from opposite side electrical train as ADV (A/B VDC) – Fail AS-IS
* Each ADV isolation valve is powered from the opposite side of its associated ADV. This ensures we will always be able to isolate each flowpath via closing the ADV itself or its’ isolation valve.

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11
Q

Describe the Main Steam Safety Valves.

A

Ensures that Secondary system pressure will be limited to 110% of its design pressure of 1000 psig for most severe transient (even without the availability of the ADV’s and the SBCS)
16 valves total – 8 safety valves per header upstream of the Main Steam Isolation Valves
First 4 valves Lift at 1000 psia; Second 4 valves Lift at 1040 psia
Steam flow equivalent capacity approx. 3034 MWT
Designed for 3% accumulation and 8% blowdown – Some questions challenge your knowledge on what pressure the safety valves should be closed at. Good rule of thumb is that they should all be closed by 900 PSIA
Using multiple safety valves protects against excessive blowdown/cooldown if one valve fails to reseat.
Decay Heat Removal can be accomplished with a minimum of 2 safeties per SG
Tech Spec requires all Safety Valves to be operable in Mode 1-3.
 With 1 or more MSSV inoperable reduce setpoint of the VHP trip within 4 hours
 Tech spec table is for max amount of MSSV’s inoperable PER steam generator
Can have a Maximum of 3 MSSV’s per SG inoperable and still stay in Mode 1

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12
Q

What is the motive force for the MSIVs?

A

Unit 1
* Electro-hydraulic Valves
* Air-driven Hydraulic Pump to OPEN
* N2 accumulator Pressure to CLOSE

Unit 2
* Air-Operated
* Basically, it is a big AOV

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13
Q

Which MSIVs will open against full system D/P?

A

Unit 2 MSIVs WILL open against full system D/P.
Unit 1 MSIVs WILL NOT open against full system D/P.

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14
Q

Describe the MSIV failure Positions.

A

Unit 1
FAIL CLOSED:
Loss of hydraulic pressure
Loss of Air (after 8 hrs if accumulator avail.)

FAIL OPEN:
Loss of DC electrical power **
** - If instrument air is aligned to the hydraulic pumps).
However, it still WILL NOT OPEN under full system dP, even on loss of power

Unit 2
FAIL CLOSED:
Loss of Air (after 8 hrs if accumulator avail.)

FAIL OPEN:
Loss of electrical power

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15
Q

Describe MSIV opening and closing.

A

Unit 1
OPENING:
Opening time 6-12 minutes
(See drawing) The MSIV consists of a two part valve arrangement with one trip valve on the inlet side and one check valve on the outlet side. The inlet trip valve is operated by the MSIV actuator. The outlet check valve (Non-return) operated by steam flow in normal direction.
When the MSIV is closed, all solenoids are energized. The MSIV opens by de-energizing all solenoids and two instrument air driven hydraulic pumps, pump the valves open by moving oil from the reservoir to the bottom of the actuator piston. (Hydraulic pumps overcome N2 pressure on top of the actuator piston)
Air Accumulators (2/valve) sized to hold MSIV’s open for 8 hours following a loss of IA.
Backup nitrogen bottle supply located on TGB 19.5’ level next to the Feedwater Isolation Valve nitrogen supply bottle racks are available as a back up source of N2 to charge the N2 accumulator.

CLOSING:
Normal Method:
N2 Accumulator pressure to CLOSE
Closing solenoids energize and blocks the oil supply to the actuator & N2 accumulator pressure closes the valve.
Alternate Method:
Locally (Manual) IAW 1-EOP-99 Appendix I which manually isolates air to the oil pumps and manually opens two dump paths. JPM to perform these actions

Unit 2
OPENING:
* For the MSIV to open, the air supply system must be functional and all solenoid valves must be de-energized
* WILL OPEN under full system differential pressure
* Has opening air port, vents the same port to close
* Angled valves with internal pilot and balance chamber with bypass which allows valve opening with full system differential pressure across it.
* The stem of the MSIV is attached to an air piston that rises against the force of four springs to open the valve
* No Non-Return Check valve – Therefore an extra MSIS trip on Hi CNMT pressure was added
* Air is supplied to or vented from only the underside of the piston to open or close the valve.
* Steam flow assists in closing, has Hydraulic Dampening System

CLOSING:
* To close the MSIV, select solenoid valves reposition particular air control valves to vent the underside of the piston

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16
Q

Describe MSIV failures.

A

Unit 1
FAIL CLOSED:
* Loss of hydraulic accumulator pressure
* Loss of Air
FAIL OPEN:
* Loss of DC electrical power (if instrument air is aligned to the hydraulic pumps).
* However, it WILL NOT OPEN under full system differential pressure, even on loss of power

Unit 2
FAIL CLOSED:
* Loss of Air

FAIL OPEN:
* Loss of electrical power

17
Q

Describe the MSIV Bypass Valves.

A

Motor operated bypass valves on each steam header used to:
* Equalize steam pressure across the MSIVs
* Warmup the Main Steam System

On Unit 1:
Bypass valve IS assured to close against reverse steam flow

On Unit 2:
Bypass valve IS NOT assured to close against reverse steam flow, therefore:
* Only one MSIV bypass can be opened at a time for steam warming (admin)
* DEFEAT/ENABLE keylock switches on MCC 2A5/2B5 for each bypass valve.
* During normal operation, the switch is in DEFEAT=bypass can’t be opened

18
Q

What is the purpose of the Main Steam Isolation Signal?

A

Shutting the MSIV’s during an ESD event minimizes the duration of uncontrolled cooldown and the resulting positive reactivity addition, ensures that at least one SG is available for RCS heat removal.

19
Q

What is the MSIS setpoint?

A

Unit 1
SG Pressure < 600 psia

Unit 2
SG Pressure < 600 psia
CNMT Pressure > 3.5 psig
 No Non-Return check valve on Unit 2 MSIV

20
Q

What does MSIS close/trip?

A

Unit 1
1) Both MSIV’s
2) Both MSIV Bypass Valves
3) All Main Feed Isolation Valves
4) Both Feed Pump Discharge Valves}
5) Both Feed Pumps}
6) Both Heater Drain Pumps}
7) Both Condensate Pumps}

Unit 2
1) Both MSIV’s
2) Both MSIV Bypass Valves
3) All Main Feed Isolation Valves

21
Q

Describe Main Steam Header Steam Traps.

A

Prevent moisture damage to turbine blades and water hammer damage to piping and fittings
Bypasses around the traps allow draining the lines should the traps become non-functional

22
Q

Describe Main Steam Header Radiation Monitors.

A

Measure mostly N-16 gammas. Assist in determining affected SG during a SGTR event.

[Unit 2 Only - Local RM-23P hookup for a portable monitor in the Turbine Switchgear Room on the east wall. Portable monitor is energized with an outlet inside the cabinet]

23
Q

Describe Moisture Separator Reheaters (MSR’s).

A
  • Improves the quality of steam and raises the enthalpy of steam entering the LP turbines
  • Improves efficiency by superheating steam before it enters the LP Turbine, 115F Superheat
  • Prevents accelerated nozzle/blade erosion in LP turbine by removing entrained moisture.
  • At ~ 30% power, begin opening reheater warm-up valves to purge non-condensable gases from reheater tubes.
  • The MSRs are placed in service when Calorimetric Power is ~ 33%.
  • Relief valves (2 per MSR) called “Buddha” Valves lift at 250 psig
  • TCV’s control Steam flow through the Reheater
24
Q

Describe the MSR Shell.

A
  • HP turbine exhaust enters the shell side of the MSRs and passes thru a bank of Chevron Moisture separators where most of the entrained moisture is removed
  • Flows over the reheater tube bundle and gains about 115F of superheat from main steam
  • Exits the MSR and continues on to the inlet of the LP turbines
  • Shell side drains are directed to either the Condenser or to the 4th Point Heater.
  • Upon MSR start-up, level starts to rise. When level increases to the Hi-Hi Level setpoint, the MSR Shell level controller starts to open the alternate drain valve and align a flowpath to the condenser.
  • Once a 50 psid is developed between the MSR shell and the 4th point heater shell, a weighted check valve opens and drainage is directed to the #4 heater shell. As level drops the alternate drain valve modulates closed.
  • MSR C & D shell side drains go to the 4A heater, A & B go to the 4B heater
25
Q

Describe the MSR Reheater Tube Side.

A
  • Main steam is supplied to the tube side via a set of block valves and TCVs
  • Motor-operated warm-up valves purge non-condensables from tubes prior to operation.
  • Passes thru an upper set of tubes, U-turns, exits at bottom as saturated liquid/steam into the Drain Collecting Tank, U-turns again into 3rd pass, U-turns into 4th pass and exits to the Steam Scavenging Vent Chamber
  • All MSR C & D tube side drains go to the 5A heater
  • All MSR A & B tube side drains go to the 5B heater
26
Q

Describe MSR Quench Water.

A
  • Quench water supplied to the MSR tube side steam drain lines to prevent flashing and water hammer in the 5th point heaters.
  • Quench water supplied from the condensate header inlet to the #5 heater
  • Quench water to the MSRs will be supplied following MSR Block Valve opening. A Solenoid valve opens ~2 minutes after the block valves open.
27
Q

Describe MSR Drain Collection Tank.

A
  • Receives condensate from the MSR tube side 2nd pass bundles
  • Upon MSR start-up, level starts to rise in the Drain Collection Tank. When level increases to the Hi-Hi Level setpoint, the Drain Collection Tank level controller starts to open the alternate drain valve and align a flowpath to the condenser.
  • Once a 55 psid is developed between the MSR Tube side and #5 HTR Shell, the Drains Collection Tank normal drain valve modulates open and aligns the drains to the #5 Heater shell. As level drops the alternate drain valve modulates closed.
  • Quench water supplied to the drain line to prevent flashing and water hammer
28
Q

Describe MSR Steam Scavenging Vent Chamber (SSVC).

A
  • Receives condensate from the MSR tube side 4th pass bundles
  • Removes non-condensable gases which reduce flow and efficiency
  • When MSR outlet temp < 400°F – Manually aligned to the condenser
  • When MSR outlet temp ≥ 400°F – Manually aligned to the #5 Feedwater Heater
  • Quench water supplied to the drain line to prevent flashing and water hammer
29
Q

Describe MSR Steam Supply Valves.

A
  • At ~100 MWe, warmup valves are used to purge the tube side of non-condensable gases
  • At ~300 MWe, motor operated block valves open to put system in operation (warm up closed)
  • Fail closed on loss of IA
30
Q

Describe MSR TCV’s & Block Valves.

A

Unit 1
* 1 - 1” warm-up valve line
* 1 - 8” line with a block valve and TCV
* TCV flow is directly proportional to position (i.e….1/2 open : 50% flow)
* Block valves auto close on a turbine trip
* All TCV’s operate together

Unit 2
* 1 - 1” warm-up valve line,
* 1 - 8” line with block valve and TCV
* 1 - 3” line with TCV and manual isolation only
* NO AUTO CLOSURE

Valves operate using a split range controller which requires the turbine to be latched.
* The 3” valve opens first, followed by the 8” valve.
* If the 3” TCV leaves full open seat, the 8” TCV will close.
* The 8” valve closes first, followed by the 3“ valve.
* 3” TCV is open but isolated at 100% power
* When the 8” TCV is half open, steam flow is at max (flow is not proportional to position)
* Block valves must be closed by operator at RTGB on a turbine trip

31
Q

Describe DEH Display 5552 Control Panel.

A

This is the main MSR Control screen which displays a diagram of the MSRs and LP turbines including tube- and shell-side valves and piping

32
Q

Describe DEH Display 5552 Control Panel Modes of Operation.

A
  • Manual – Operator pushes button to change demand.
  • Automatic Temp – Operator selects ramp rate from 0 - 75°F per hour until target temp (525°F) reached
  • Auto Time - Operator selects target time to get TCV’s 100% open from 120-600 min
  • Ramp Down - Closes TCVs over 60 minutes (from full open). Resets when TCV reaches 0.5% open
  • Reset - Terminates other temperature controller modes and fully shuts TCVs. Requires load ≤ 25% (257.5 MWe) to manually select. Reset is automatic on turbine trip and during Ramp Down when TCV reaches 0.5% open. Remove Reset signal by selecting Manual, Auto Temp or Auto Time mode
33
Q

What are the MSR heat up limits?

A

a) A maximum heatup of 25°F over a 20 minute period
b) A maximum heatup rate of change of 75°F / hr.

34
Q

Describe Extraction Steam Function.

A
  • Increases overall efficiency by using energy that would otherwise be lost to the main condenser
  • Heater # 5 HP Turbine between 5 & 6 stages (shell drains to #4 shell)
  • Heater # 4 HP Turbine Exhaust
  • Drains Cooler No Extraction Supplied
  • Heater # 3 LP Turbine Third Stage
  • Heater # 2 LP Turbine Fifth Stage (no NRV-minimal DP b/w htr & turbine)
  • Heater # 1 LP Turbine Sixth Stage (no NRV-minimal DP b/w htr & turbine)
  • Pre-Heating of the feedwater gains Efficiency and minimizes Thermal Shock to the SGs
  • Feedwater Temperature is raised from 110F to 435F
35
Q

Describe the functions of the Non-Return Check Valve on #5, 4, 3 Heaters.

A
  • Prevent high water level in heater from backing up into the turbine, causes damage to turbine blades.
  • Prevent backflow of steam into the turbine following a trip, prevents over speeding the turbine.
  • Air Bleeds off the Cylinder allowing a spring actuator to knock the weighted check off of the full open seat to ensure it is not stuck and will go closed on reverse flow
  • Closes on: Turbine Trip, OPC (Overspeed Protection Circuit), Heater Hi Hi Level
36
Q

Describe the [Extraction Steam Drain Line Bypass Valve - Unit 2 Only] - #3, 4 & 5 Heaters only.

A
  • Air Operated Drain that taps into the extraction steam line upstream of the Manual Isolation Valve and the NRV and drains to the Condenser
  • Drain Valve Opens on High Level in the Drip Leg
  • Valve goes full open (does not throttle)
  • Valve will not close when Hi Water Level clears - Operator must close valve from RTGB
  • High Level indicated by AMBER Light above the valve position indication and control PB’s on RTGB
37
Q

Describe the Auxiliary Steam Function.

A

There are {5} [3] Reducing Stations that reduce main steam pressure to:
* 400 psig For SJAE (fails open)
* 200 psig For Main Condenser Waterbox Aux Priming Ejectors (fails closed)
* 25 psig For Aux Bldg Supply (Not used) (fails closed)

  • 12 Temperature Switches that sense RAB Temperature will isolate Aux Steam to the RAB @ 150F

Main Steam is manually throttled down to 200 psig for:
* Main Condenser Waterbox Priming Ejectors
* Hogging Air Ejectors

38
Q

Describe Air Ejector Miscellaneous Information.

A
  • Aux priming ejectors normally in service, help remove non-cond. gas from the Waterbox (CW)
  • Priming ejector only used during startup to aid in drawing a Waterbox vacuum.
  • Hogging ejector used to draw an initial vacuum on the main condenser
  • SJAE used to maintain the vacuum on the main condenser

Block 4 (7 decks)

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